Data operations are not allowed in Full Mode.
If an API user is in full development mode, data operations are not allowed. The user needs to perform these operations either in Base Development mode or overlay mode.
So, from that I'm wondering if the user that you are running as on your 8.1 server has access to be in base mode, this can be found out by logging into Dev Studio as that user and try to switch to base mode...if that works, then I'm not sure what this is saying.
I dont see any issues in Dev Studio, its working fine
It works now, as I have ARS 8.1 I am using BPCU 8.1 now and its working so far.